At low levels, carbon monoxide (CO) has physiological roles as a second messenger and neuromodulator1,2. Here we assess the effects of CO in a mouse model of traumatic brain injury (TBI). Treatment with CO-releasing molecule (CORM)-3 reduced pericyte death and ameliorated the progression of neurological deficits. In contrast, although treatment with the radical scavenger N-tert-butyl-a-phenylnitrone (PBN) also reduced pericyte death, neurological outcomes were not rescued. As compared to vehicle-treated control and PBN-treated mice, CORM-3-treated mice showed higher levels of phosphorylated neural nitric oxide synthase within neural stem cells (NSCs). Inhibition of nitric oxide synthase diminished the CORM-3-mediated increase in the number of cells that stained positive for both the neuronal marker NeuN and 5-bromo-2′-deoxyuridine (BrdU; a marker for proliferating cells) in vivo, consequently interfering with neurological recovery after TBI. Because NSCs seemed to be in close proximity to pericytes, we asked whether cross-talk between pericytes and NSCs was induced by CORM-3, thereby promoting neurogenesis. In pericyte cultures that were undergoing oxygen and glucose deprivation, conditioned cell culture medium collected after CORM-3 treatment enhanced the in vitro differentiation of NSCs into mature neurons. Taken together, these findings suggest that CO treatment may provide a therapeutic approach for TBI by preventing pericyte death, rescuing cross-talk with NSCs and promoting neurogenesis.
This work was supported in part by grants from the US National Institutes of Health (K.H., K.A., M.J.W., C.X., X.W. and E.H.L.), the Rappaport Foundation (E.H.L.), the Research Abroad grant from the National Research Foundation of Korea (Y.K.C., S.-H.K., Y.-M.K. and K.-W.K.) and the Global Research Laboratory Program of Korea (K.-W.K.). The vector expressing the HIF-1α double mutant was kindly provided by G.L. Semenza (Johns Hopkins University School of Medicine).
Supplementary Figures 1–8